How does it work?
Well, vinegar is an acid, and it reacts with the salt to remove what chemists call copper oxide (the stuff that makes your pennies dull).

But there’s more you can do!
Add more pennies to your bowl and count slowly to ten again. When you remove them, don’t rinse them off. Just put them on paper towels to dry. Shortly, the pennies will turn blue/green as something called malachite forms on the pennies.

There’s even more!Put a few nuts and bolts in the vinegar and watch them carefully; they may turn copper in color. The vinegar will remove copper from the pennies and if there’s enough of it in the vinegar — the copper will become attracted to the metal in the nuts and bolts!